allow clients to be able to connect.nano /etc/hosts.allow
add lines like:portmap: 192.168.0.0/255.255.0.0
add clients to hosts filenano /etc/hosts
make sure all relevant hosts are listed in the format:192.168.x.x server1.domain.com.local server1

The -- -f section is used to plug in a sender address, otherwise the mail will be sent from your root or user account from the actual physical server name - e.g root@server1.domain.com

This comes in handy for notification of script execution, for example, jobs in the crontab. Placing this code immediately after the last command in a shell script will ensure relevant person(s) are notified when the script is called.